1. Field of the Invention
The present invention relates to a one-way spring coupler through which rotation is transmitted from a drive member to a driven member but rotation is not reversibly transmitted.
2. Description of the Prior Art
FIG. 1 and FIG. 2 show a conventional spring coupler 10. The spring coupler 10 comprises a base member 14, a drive member 11 and a driven member 12 rotatably disposed in the base member 14, and a spring member 13 mounted in the base member.
The drive member 11 has a recessed portion 11a and the driven member 12 has a projecting portion 12a. The projecting portion 12a is engaged with the recessed portion 11a through predetermined clearances 15a, 15b so that the drive member 11 and the driven member 12 can be rotated as a whole. The spring member 13 is frictionally connected to the inner surface of cylindrical sidewall 14a of the base member 14. Both end portions 13a, 13b of the spring member 13 are bent inwardly so to form tangs respectively engageable in the clearances 15a, 15b with edge portions 11b, 11c of the recessed portion 11a of the drive member 11.
Thus, in FIG. 2, in case the drive member 11 is rotated in the clockwise direction, the edge portion 11c is engaged with the tang 13b of the spring member 13. In case drive member 11 is rotated in the counter-clockwise direction, the edge portion 11b is engaged with the tang 13a of the spring 13. In each case, by rotating the drive member 11 the spring member 13 is tightened about the drive member 11 so that the spring member is released from frictional contact with the inner surface of sidewall 14a and the frictional connection there between is canceled. After the frictional contact is released, the recessed portion 11a of the drive member 11 abuts against the projecting portion 12a of the driven member 12 through the tang 13a or 13b of the spring member 13, in accordance with the direction of rotation of the drive member 11, and the driven member is rotated by the drive member.
On the contrary, in case driven member 12 is rotated in the clockwise or counter-clockwise direction, the projecting portion 12a of the driven member 12 abuts against one of the tangs 13a, 13b of the spring member 13. By the rotation of the driven member 12, the spring member is expanded so that the spring member 13 is more frictionally connected to the inner surface of the sidewall 14a and the frictional connection between the spring member and the inner surface of the sidewall 14a is securely maintained. Thus, the counterrotation of the drive 11 member by the driven member 12 is obstructed. The rotation of the driven member 12 is not transmitted to the drive member 11 and the driven member 12 is maintained at a predetermined position.
However, in the conventional spring coupler 10, a certain amount of clearance 15a, 15b between the recessed portion 11a and the projecting portion 12a is required. If clearance 15a, 15b is not enough, the recessed portion 11a of the drive member 11 immediately abuts against the projecting portion 12a with the rotation of the drive member 11 and the driven member 12 is rotated without proper tightening of the spring member 13. Since the counterrotation of the driven member 12 must expand the diameter of the spring member 13 to maintain the drive member 11 against counterrotation, the driven member will act on the drive member through a tang of the spring 13 and counterrotate the drive member.
On the other hand, if the clearances 15a, 15b are too large, there will not be sufficiently positive action between the drive member 11 and the driven member 12 and there will be a tendency toward oscillation of the drive member 11 and driven member 12 with respect to each other.